In eukaryotic organisms the generation of functional cytoplasmic messenger RNA from nuclear gene transcripts appears to be a complex process. The proposed research project is designed to provide detailed structural and functional information about this process in the case of a single mRNA of known function, namely the mRNA which codes for silk fibroin in the silkworm Bombyx mori. A method has been developed which should permit the isolation of sild fibroin gene transcripts from complex RNA mixtures, such as total nuclear or total cellular RNA. It is based on affinity chromatography in a column containing a synthetic polynucleotide capable of forming hybrids with silk fibroin mRNA. The column will be used to isolate newly-synthesized (nuclear) transcripts of te silk fibroin gene. The characterization of these molecules, and a comparison of their structure and sequence content with that of cytoplasmic mRNA will be undertaken. Efforts will also be directed towards using the affinity column for the isolation of fibroin messenger ribonucleoprotein particles from subcellular fractions or from whole cell homogenates. Nuclear fibroin mRNP and cytoplasmic fibroin mRNP will be purified by affinity chromatography and by equilibrium density centrifugation in order to study their structure and the properties of the associated polypeptides. Comparisons will also be made between the polypeptides of fibroin and non-fibroin mRNP. Attempts will be made to obtain information about fibroin mRNP structure by electron microscopy.